Headbox for paper machine



9, 1965 P. B. WAHLSTROM ETAL 3,215,392

HEADBOX FOR PAPER MACHINE 2 Sheets-Sheet 1 Filed April 9, 1963 V .II

INVENTQBS: PER BORJE WAHLSTROM ERIK GUNNAR STENBERG BY mfiwwrm THEIR ATTORNEYS 1965 P. B. WAHL STRGM ETAL 3,216,892

HEADBOX FOR PAPER MACHINE 2 Sheets-Sheet 2 Filed April 9, 1963 FIGZ.

INVENT RS:

PER BSRJE WAH'LSTR ERIK GUNNAR STENBERG THEIR ATTORNEYS United States Patent 3,216,892 HEADBOX FOR PAPER MACHINE Per Biirj e Wahlstriim and Erik Gunnar Stenberg, Karlstad, Sweden, assignors to Aktiebolaget Karlstads Mekaniska Werkstad, Karistad, Sweden, a company of Sweden Filed Apr. 9, 1963, Ser. No. 271,655 Claims priority, application Sweden, Apr. 12, 1962, 4,075/62 4 Claims. (Ql. 162343) The invention relates to a headbox of a paper machine, where a flow of pulp is spread or evened out in the cross direction of the machine through a hole-plate.

At such a headbox the pulp flows as parallel jets with high velocity into the space behind the hole-plate where the velocity of the pulp is lower and because of that an unstable flow is obtained. In order to establish the best possible distribution of the flow by means of the hole-plate the drop of pressure in the holes should be relatively large in order to reduce the influence on the distribution from the occurring variations of the pressure in the pulp at the inlet side of the hole-plate. This usually means that the hole-plate will have a small open area and that the velocity of the jets ejecting through the holes will be many times larger than the average velocity of the pulp in the headbox after the hole-plate. The decay of these high velocity jets against the surrounding, slower moving pulp may cause irregular vortices and cross flows. The object of the present invention is to provide means for a pulp flow free of interferences.

The fundamental embodiment of the invention is an obstacle placed in the flow direction behind and close to the hole-plate. The obstacle is provided with solid impact surfaces in front of the holes of the hole-plate and open areas displaced in relation to the holes of the hole-plate, so that the high velocity jets can not pass the obstacle without being deflected. The jets of pulp coming from the hole-plate are divided and damped by the obstacle in uniform manner so that the kinetic energy of the jets can not cause instability in the flow but is transformed to a harmless turbulence in the pulp close to the hole-plate.

The said obstacle may preferably consist of a second hole-plate with a higher degree of open area than the first hole-plate. The hole-plates are preferably arranged in parallel with an interspace not exceeding times the distance between the centre lines of the holes of the holeplates. Hereby the mixing region, which otherwise would extend far into the subsequent part of the headbox, is shortened and concentrated mainly to the interspace between the hole-plates. Through the holes of the second hole-plate, which are as many as the holes of the first plate but larger the pulp flows as comparatively thick and slow jets into the subsequent part of the headbox. In case also these mild jets may cause instability, necessary steps according to the invention may be provided in order to neutralize this instability. These steps may e.g., provide for a third hole-plate with still larger open area and arranged after the second hole-plate. The holes of the third hole-plate are to be placed concentric to the holes of the first hole-plate and consequently displaced in relation to the holes of the intermediate second plate.

The invention will hereinafter be described in detail with references to the accompanying drawings. FIG. 1 shows diagrammatically and in perspective a headbox embodying the invention. FIG. 2 is an enlarged fragmentary side view of the arrangement of the hole-plates against the flow direction of the pulp. FIG. 3 is a horizontal section on the line IIIIII of FIG. 2. FIG. 4 is a similar horizontal section of a modified arrangement of the hole-plates.

The headbox shown on FIGURE 1 belongs to a Fourdrinier paper machine and is intended to spread pulp over a wire 11 as a wide and thin jet with approximately the same speed as the speed of the wire. The pulp is fed into the headboX by a pipe 13 in a direction preferably across the direction of the machine. In the wall of this pipe is arranged a hole-plate 15 provided with a great number of horizontal holes 27 extending in the longitudinal direction of the machine. The hole-plate 15 forms the back wall of the headbox, which also comprises a plane horizontal bottom 17 approximately as wide as the wire 11, a cover 19 in parallel to the bottom 17, two vertical side walls 21, 23 and a forward sloping front wall 25. Between the lower edge of the wall 25 and the bottom 17 a nozzle is formed, through which the pulp will be spread out over the wire 11.

The pipe 13 has a rectangular cross section with a constant height but its width decreases continuously over the entire length of the hole-plate and remains thereafter constant. The quantity of pulp not passingthrough the holeplate 15, flows in an unaltered direction out through the narrow end of the pipe 13 and is then recirculated. The shape of the pipe 13 provides for a constant speed of the flow of the pulp in the pipe and consequently an even pressure of the pulp along the entire length of the holeplate 15.

As shown in FIGS. 2 and 3 the hole-plate 15 is provided with a great number of holes 27 arranged in vertical and horizontal rows. The holes are long and at their ends facing the pipe 13 conical. The holes are so narrow and spaced so far between that the total area of the holes is only a small fraction of the total area of the hole-plate, e.g., from one tenth to one third. The pulp will therefore flow out through the hole-plate as jets with a velocity many times the average velocity of the pulp in the subsequent part of the headbox. These jets would be able to reach far until they finally would be stopped by the surrounding slower moving pulp and they should be able to cause instability in the flow if the arrangements described below and embodying the invention had not been provided.

Downstream from the hole-plate 15 is another holeplate 29 arranged across the headbox. This hole-plate 29 has the same length and height as the hole-plate 15 and is placed in parallel with and at a distance from the hole-plate 15 of 30 to mm., preferably about 50 mm. The hole-plate 29 is provided with holes 31 in the same number and pattern as the hole-plate 15, but the holes 31 are displaced horizontally as well as vertically half a graduation in relation to the corresponding holes 27. A jet flowing perpendicular from the hole-plate 15 through a hole 27, will therefore impinge against the holeplate 29 at a place situated between and at about the same distance from four holes 31. The holes 31 are wider than the holes 27. The strong jets coming from the holeplate 15 will therefore be split and deflected and an intensive mixing of the pulp will take place in the space between the two hole-plates. The pulp flowing out from this space is, by passing the hole-plate 29, again divided up into jets. However these jets are wider and have considerably lower velocity than the jets coming from the holes 27 and may therefore only slightly be able to cause instability in the pulp flow in the subsequent part of the headbox.

In order to remove remaining tendency if any for disturbances from cross flows a number of parallel, closely spaced vertical guide vanes 33 are placed adjacent to the hole-plate 29 between the bottom 17 and the cover 19 of the headbox in the machine direction, i.e. in the flow direction of the headbox. The center distance between the guide vanes is a multiple of the horizontal center distance between the holes of the plate 29 and the guide vanes are consequently uniformally spaced with respect to the holes. At the arrangement shown in FIG. 2 the guide vanes 33 are placed right in front of every second vertical row of holes, but they may of course also be placed between the rows of the holes, so that they at their entire height fit-up against the hole-plate 29. In certain cases satisfactory flow conditions may be obtained without the guide vanes 33 and they may in such cases be omitted.

The above mentioned guide vanes may be substituted by a third hole-plate as shown in FIG. 4. The third holeplate 35 will have a still larger open area than the holeplates 15 and 29 and a corresponding hole-pattern. The holes 37 are wider than the holes 31 and are displaced in relation to these half a graduation vertically as well as horizontally and they will therefore lie concentric to the imaginary extensions of the holes 27 of the first holeplate 15. The thick jets flowing out through the holes 31 will at least with their central parts impinge against the solid sections between the holes of the hole-plate 35 and will be split and deflected so that a repeated mixing of the pulp occurs between the hole-plates 29 and 35. The pulp flowing out through the holes 37 is therefores still more evened out and unidirected. Also by this arrangement guide vanes may be used if required.

Within the scope of the invent-ion further modifications of the shown arrangements are possible. The holeplate 29 or 35 may be substituted by an obstacle consisting of a number of parallel rods. The rods may preferably be placed in front of the rows of holes of the preceding hole-plate, so that the jets will be split by the rods and the pulp will pass the slot shaped spaces between the rods after deflection.

We claim:

1. A headbox for a paper machine, comprising a first hole-plate having a plurality of holes through which pulp can flow in a plurality of jets, said holes being separated by land areas, a second plate substantially parallel with said first plate and; downstream from and adjacent thereto, said second hole plate land areas in register with the holes of said first hole-plate against which the jets from said first hole-plate impinge, and said second-plate having open areas out of register with and substantially equal in number to and of greater total area than said holes of said first hole-plate so that jets of said pulp from said holes are deflected laterally before said pulp can pass through said open areas.

2. A headbox as in claim 1 in which said first and second hole-plates are substantially parallel with an interspace not exceeding five times the distance between the center lines of the holes in said first hole-plate.

3. A headbox as in claim 1 comprising a plurality of parallel guide vanes adjacent to and downstream of the second hole-plate and substantially perpendicular thereto.

4. A headbox as in claim I comprising a third holeplate having holes wider than the holes of the second hole-plate and located in register with the holes of the first hole-plate and out of register with the holes of said second hole-plate.

References Cited by the Examiner UNITED STATES PATENTS 2,677,991 5/54 Goumeniouk 162343 2,688,905 9/54 Hornbostel 162-343 2,881,674 4/59 Johnson et al. 162-2l6 2,929,449 3/60 Mardon et al. 162337 3,092,540 6/63 Parker 162 336 3,103,463 9/63 Justus 162341 3,119,733 1/64 Wilson et al. 162336 FOREIGN PATENTS 109,005 11/43 Sweden.

DONALL H. SYLVESTER, Primary Examiner. 

1. A HEADBOX FOR A PAPER MACHINE, COMPRISING A FIRST HOLE-PLATE HAVING A PLURALITY OF HOLES THROUGH WHICH PULP CAN FLOW IN A PLURALITY OF JETS, SAID HOLES BEING SEPARATED BY LAND AREAS, A SECOND PLATE SUBSTANTIALLY PARALLEL WITH SAID FIRST PLATE AND; DOWNSTREAM FROM AND ADJACENT THERETO, SID SECOND OLE PLATE LAND AREAS IN REGISTER WITH THE HOLES OF SID FIRST HOLE-PLATE AGAINST WHICH THE JETS FROM SAID FIRST HOLE-PLATE IMPINGE, AND SAID SECOND-PLATE HAVING OPEN AREAS OUT OF REGISTER WITH AND SUBSTANTIALLY EQUAL IN NUMBER TO AND OF GREATER TOTAL AREA THAN SAID HOLES OF SAID FIRST HOLE-PLATE SO THAT JETS OF SAID PULP FROM SAID HOLES ARE DEFLECTED LATERALLY BEFORE SAID PULP CAN PASS THROUGH SAID OPEN AREAS. 